1. Technical Field of the Invention
The present invention relates to interconnection of a number of private branch exchange (PBX) systems, and more particularly, to communications between PBX systems that do not require day/night notifications to enable efficient call transfer from one PBX to another.
2. Description of Related Art
One manner in which PBX systems provide flexible and effective operator service is through the use of a centralized operator function and a day/night status notification function. These functionalities enable a satellite PBX to know the status of attached central PBXS. The day/night status notification function provides the satellite PBX with a notification of whether a central PBX is in the day or night operational status.
During the day status, the central PBX is opened to receive calls and has human operators in place such that any call which is redirected from a satellite PBX may be completed. The night status indicates that the central PBX is presently not manned by a human operator. Thus, calls to numbers served by the satellite PBX shall not be redirected to the central PBX. The day/night status notification function within the central PBX notifies the satellite PBX of the status of the central PBX and the satellite PBX can refer to this information to select a new destination for directing calls of the satellite PBX while it remains in night status.
The centralized operator function of a PBX system requires the support of the day/night status notification functions from the central PBXs in order to know the status of the various PBXs to which a satellite PBX is connected. In order to synchronize the day/night status data between the central and satellite PBXs, periodic notifying and updating are necessary. However, within a large private network, a central PBX may limit the number of satellite nodes which it notifies of its own day/night status in order to prevent adverse affects upon the private telecommunication network's overall performance.
Also, no matter how often the notification is executed, there always exist a window between the time the status of a central PBX changes and the satellite PBX is notified. The situation may occur where a call is transferred from a satellite PBX to a central PBX whose status may have just changed. A method for eliminating the possibility of improper call connection attempts to PBX systems and for limiting housekeeping communications between PBX systems would be a very valuable improvement for PBX systems.